The present invention relates to a process for producing 6-dimethylaminomethyl-1-(3-hydroxy- or 3-C1-C4 alkoxyphenyl)-cyclohexane-1,3-diols from 6-dimethylaminomethyl-1-hydroxy-1-(3-hydroxy- or 3-C1-C4 alkoxyphenyl)-cyclohexane-3-ones by catalytic hydrogenation in the presence of heterogeneous or homogeneous catalysts, or by using metal hydrides.
U.S. Pat. No. 5,733,936 (=EP 753,506) discloses 6-dimethylaminomethyl-1-(3-hydroxy- or 3-C1-C4 alkoxyphenyl)-cyclohexane-1,3-diols which are effective analgesics, suitable in particular for the treatment of intense pain. These compounds have 3 asymmetric carbon atoms. The 6-dimethylaminomethyl-1-(3-hydroxy- or 3-C1-C4 alkoxyphenyl)-cyclohexane-1,3-diols are obtained by hydrogenating corresponding racemic 3-cyclohexanones with metal hydrides, such as sodium borohydride (Example 18) or diisobutylaluminium hydride (Example 20), and separation of the racemates thus formed by means of HPLC on chiral columns then yields the 1R,3R,6R and 1S,3S,6S stereoisomers. This method of production of enantiomer-pure compounds is not particularly advantageous for industrial applications. It is also known that both the aforementioned cyclohexane-1,3-diols and the starting materials (3-cyclohexanones) decompose slightly, or rather tend to undergo elimination reactions with the formation of unsaturated compounds. Owing to this sensitivity of the compounds, the formation of undesirable by-products during hydrogenation may be so high, or even predominate (such as when reducing with diisobutylaluminium hydride), that these reactions are not particularly economical and are thus less suitable for the industrial production of pharmaceutical active ingredients.
It has been found that some stereoisomers are characterized by particularly good efficacy. These stereoisomers are 1R,3R,6R and 1S,3S,6S stereoisomers of formulas III and IV or mixtures thereof

The 1R,3S,6R and 1S,3R,6S stereoisomers of formulas V and VI
are, in contrast, less desirable and their formation should thus be avoided as far as possible during production.